iSpring RCC7AK-BN NSF Certified, 75 GPD, Alkaline 6-Stage Reverse Osmosis System, pH+ Remineralization RO Water Filter System Under Sink Patented Top-Mounted Faucet Design for Easy Installation

Why it's worth it

The RCC7AK-BN is a six-stage RO system that adds calcium and magnesium back after the membrane strips them out, so the water tastes like water instead of nothing. The whole system, not just the membrane, is certified to NSF/ANSI 58.

Plenty of people install RO, take a drink, and think something's missing. They're right. The membrane pulls out nearly everything, minerals included, and the result can taste flat and slightly hollow. The sixth stage here runs purified water through calcite and coconut-shell carbon, which lifts pH to roughly 7.5 to 8.5 and returns calcium and magnesium. It's the direct fix for the most common complaint about RO water.

Full-system certification is rarer than the marketing implies. Many brands certify a single component and let you assume the rest is covered. iSpring has the complete RCC7AK certified to NSF/ANSI 58. The published reduction figures are specific, too: 93 to 98 percent of TDS, 96 to 99 percent of PFAS, more than 98.9 percent of lead, and over 97 percent of fluoride, along with asbestos, barium, cadmium and chromium.

From our review of 7 under-sink water filtration systems

What we like

• +Plenty of people install RO, take a drink, and think something's missing
• +Full-system certification is rarer than the marketing implies
• +Installation is friendlier than most tank systems
• +The clear first-stage housing is a small touch that pays off

What to know

• –It's a 75-gallon-per-day system with a storage tank, and that combination has consequences in a real cabinet
• –Six stages means six things to replace on staggered schedules